How much water should you drink?

Ask anybody this question, including health care professionals, and a confident response will be back at you in a flash … “2 litres a day” … “8 glasses a day” ... "only water counts as water”, some may add. 
 
We’ve all read it and heard it so many times before, so it must be true, right? Too many people say it for it to be wrong, right? If it isn’t true, then somebody would be saying it isn't true, wouldn't they?​

Drinking of 2 litres of fluid in a day is not going to be harmful for anyone who has healthy kidneys – fluid intake is restricted in some people with impaired renal function. One of the roles of our kidneys is to regulate the amount of water in our body. ​

​These marvellous organs (well, all our organs are quite marvellous) can remove between half a litre and 23 litres of fluid a day, but drinking an excessive volume of fluid over a short period of time overwhelms renal capacity to excrete water, and this can be fatal.

We definitely should not be consuming fluid at a rate that exceeds our kidneys’ rate of getting rid of excess water, which is, say, about 1 litre an hour. And why would anybody ever need to drink more than 1 litre in an hour?

When and from where did the ‘recommendation’ to drink 2 litres of water a day find its way into all the lifestyle publications of today?

It may have originated back in 1945 when the US Food and Nutrition Board of the National Research Council (NRC) issued a recommendation for meeting our fluid requirement: 

"An ordinary standard for diverse persons is 1 millilitre for each calorie of food. Most of this quantity is contained in prepared foods." [1]

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​Note that last sentence. It’s important, yet is overlooked by lifestyle gurus, and many health care professionals – sorry, my dear colleagues! Translating that NRC rec: someone who consumes 2000 calories a day requires 2 litres of fluid a day and most of that fluid is available from food. 

The bottom line is that water in food counts just as much as does water drunk from a glass, or sipped from a personalised designer water bottle, or in trendy ice cubes imported from Japan’s Mount Haku (yes, I know). Chemically, it’s all the same stuff.

​The water you add when cooking rice, pasta or other grains counts. The water in the milk you add to breakfast cereal counts. The water in yogurt counts. The water in fresh, frozen, and canned fruits and vegetables, as well as in salads, counts. And let’s not forget the water in tea, coffee, and juices. It all counts.

Eat well. Add lots of salad veg or cooked veg to your meals. Eat fresh fruit a few times a day, carry on enjoying your tea, coffee and the rest, and you won’t need to drink anywhere near 8 glasses of water to meet your daily fluid requirement. 

​​Urine colour can be an indicator of hydration status. Aim to drink the amount of fluid needed to pass pale yellow pee around 5 times a day – do remember that certain vitamin supplements and medications can affect urine colour.

​​Cheers!

Tony Hirving
Dietitian

1 Culinary Arts/Basics/Nutrition/The Basics/Water - Wikibooks, open books for an open world